Each year tens of millions of gallons and more of contaminated aqueous solutions are discharged as industrial wastes. These solutions contain a variety of contaminants including heavy metals and sulfates, substances which are objectionable from an environmental standpoint. Typical examples of industries which generate and discharge waste solutions containing contaminants such as the above mentioned heavy metals and sulfates include the chemical, metal processing and mining industries.
Due to the real as well as the potential adverse impact that such contaminants as heavy metals and sulfates do and can have on man and environment, both federal and state agencies have promulgated and put into force numerous regulations establishing maximum concentration levels for these contaminants in industrial waste solutions discharged into our groundwater systems.
In order to comply with these regulations, a number of processes have been used or are now undergoing testing and development to effect removal of various contaminants, including the removal of heavy metals. Such processes include gravity sedimentation, flotation, filtration, ion exchange, activated adsorption, reverse osmosis, electrodialysis, distillation and chemical precipitation. However, many of these processes are not ideally suited to treat large volumes of water or are excessively expensive to install and operate in comparison with their overall efficiency and effectiveness.
In addition to the above processes, various biological processes are known for specifically removing heavy metals and sulfates from waste water solutions. In such processes, sulfate reducing bacteria are employed to reduce the sulfates to hydrogen sulfide which in turn reacts with the heavy metals to form water insoluble heavy metal sulfides which precipitate out of solution. Typical examples of known biological processes for removing heavy metal and sulfate contaminants from byproduct aqueous waste streams or solutions are described in U.S. Pat. No. 4,354,937 and U.S. Pat. No. 4,108,722.
Drawbacks to the use of such biological processes, however, also are well known. These include, to illustrate but a few, the production of metabolic wastes which in and of themselves represent real or potential pollution problems and the formation of finely crystalline sulfide precipitates the removal of which, by sedimentation or filtration, is extremely difficult.